title: A severe form of abetalipoproteinemia caused by new splicing mutations of microsomal triglyceride transfer protein (MTTP).
abstract: Abetalipoproteinemia is a rare autosomal recessive disease characterized by low lipid levels and by the absence of apoB-containing lipoproteins. It is the consequence of microsomal triglyceride transfer protein (MTTP) deficiency. We report two patients with new MTTP mutations. We studied their functional consequences on the triglyceride transfer function using duodenal biopsies. We transfected MTTP mutants in HepG2 and HeLa cells to investigate their association with protein disulfide isomerase (PDI) and their localization at the endoplasmic reticulum. These children have a severe abetalipoproteinemia. Both of them had also a mild hypogammaglobulinemia. They are compound heterozygotes with c.619G>T and c.1237-28A>G mutations within the MTTP gene. mRNA analysis revealed abnormal splicing with deletion of exon 6 and 10, respectively. Deletion of exon 6 (Δ6-MTTP) introduced a frame shift in the reading frame and a premature stop codon at position 234. Despite the fact that Δ6-MTTP and Δ10-MTTP mutants were not capable of binding PDI, both MTTP mutant proteins normally localize at the endoplasmic reticulum. However, these two mutations induce a loss of MTTP triglyceride transfer activity. These two mutations lead to abnormal truncated MTTP proteins, incapable of binding PDI and responsible for the loss of function of MTTP, thereby explaining the severe abetalipoproteinemia phenotype of these children.
authors.affiliation: INSERM/UMR 1048, Institut de Maladies Métaboliques et Cardiovasculaires, Université de Toulouse III, Toulouse, France.
authors.forename: Véronique
authors.initials: V
authors.lastname: Pons
authors.forename: Corinne
authors.initials: C
authors.lastname: Rolland
authors.forename: Michel
authors.initials: M
authors.lastname: Nauze
authors.forename: Marie
authors.initials: M
authors.lastname: Danjoux
authors.forename: Gérald
authors.initials: G
authors.lastname: Gaibelet
authors.forename: Anne
authors.initials: A
authors.lastname: Durandy
authors.forename: Agnès
authors.initials: A
authors.lastname: Sassolas
authors.forename: Emile
authors.initials: E
authors.lastname: Lévy
authors.forename: François
authors.initials: F
authors.lastname: Tercé
authors.forename: Xavier
authors.initials: X
authors.lastname: Collet
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Mas
mesh_terms: D000012:Abetalipoproteinemia / Q000235:genetics* / Q000473:pathology*; D000361:Agammaglobulinemia / Q000235:genetics; D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002648:Child; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005091:Exons / Q000235:genetics*; D005260:Female; D006367:HeLa Cells; D056945:Hep G2 Cells; D006801:Humans; D007223:Infant; D008297:Male; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D019704:Protein Disulfide-Isomerases / Q000235:genetics / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D014280:Triglycerides; C106092:microsomal triglyceride transfer protein; D019704:Protein Disulfide-Isomerases